A diamond drill consists of a power unit rotatingly driving a tubular steel bit. Diamonds are set into the face of the bit so as to allow drilling into rock or the like. The bit and an attached core barrel are rotated at speed under controlled longitudinal pressure by means of rotating hollow, steel, flush-jointed rods threaded onto the core barrel. Water is pumped through the rods to cool the bit and to remove rock cuttings.
With the advance of the bit through the rock, a cylindrical core of rock passes up into the core barrel. Two types of rod strings are in current use, "standard" and "wireline".
In "standard" drilling, when the core barrel is full of core or blocked in such a manner as to prevent further core from entering the core barrel, the rod string is pulled out of the hole and the core is removed from the core barrel and placed in boxes suitable for examination and storage. The core barrel and rod string are then put back down the hole and drilling continues.
In "wireline" drilling the core is collected in a thin walled inner core barrel which is resident inside the thick outer core barrel. Drilling continues until the inner core barrel is full or blocked in such a manner as to prevent further core from entering the core barrel. This inner core barrel, full of the cut core, may be retrieved by passing a special tool, which is connected to a thin cable, down the centre of the rod string. The inner core barrel is hoisted up without the removal of the rod string from the hole and an empty inner core barrel is pumped down to the bottom of the hole to replace it. Drilling continues. The core from the inner core barrel is emptied into boxes suitable for examination and storage.
In both cases, it is required to pull the rod string for many reasons: when changing the bit, when the bit is clogged, when the hole is finished, when setting a wedge, etc.
A conventional diamond drill arrangement typically consists of a steel motor-mount frame on which is mounted a conventional gasoline or diesel motor which, through a clutch and transmission, supplies power to a drum for hoisting drill rods and which also supplies power to the drill head so as to rotate the drill rod in the drill hole. The drum winds a wire cable through a wheel at the top of a second bore hole head frame, erected over the drill hole, so as to enable the hoisting of the drill rods out of the drill hole. The cable is typically removably attached to the drill rods by means of a hoisting plug.
Two types of drilling heads are in common use, a screw feed head and a hydraulic feed head. In both arrangements power is transmitted from the motor through a transmission and clutch to a set of crown and bevel gears. In the screw feed arrangement, the feed screw rotates so as to rotate the rods, core barrel and drill bit. In the screw feed head, an arrangement of gears rotates the feed screw so as to advance the drill rods longitudinally. At the bottom of the feed screw is a multiple-jawed chuck through which the drill rods pass. The chuck jaws are manually clamped onto the drill rod so as to hold the drill rod in the feed screw.
During drilling operations, when the feed screw has run its full length, the chuck is loosened and the feed screw and chuck run back through the gearing in the drilling head so as to engage the next length of drill rod by the manual tightening of the chuck jaws onto the drill rod. This operation continues for five to ten feet or until the capacity of the core barrel has been reached.
When "standard" rods are used, the drill rods are then hoisted up to the top of the frame and then removed, usually in twenty- or thirty-foot sections, until the core barrel is eventually pulled to the surface and disconnected. The bit is then detached and the core removed from the core barrel. The bit and core barrel are then reattached to the drill rods, the drill rods lowered into the hole, and the whole process is then repeated.
When "wireline" rods are used, the rod string is pulled out of the drill hole until the first available joint is reached. The rods are disconnected at this joint, and a latch device, to which a thin cable is attached, is dropped or pumped down the hole to retrieve a thin inner core barrel which contains the core. The inner core barrel is hoisted out of the rod string and an empty one is pumped to the bottom of the hole. In this manner drill holes up to thousands of feet long (at least for geological surveying) are advanced into the bedrock.
The hydraulic drill head arrangement merely replaces the screw feed with hydraulic rams for urging the drill rod longitudinally into, or out of, the drill hole. Again, the drill rod is held in a chuck. One additional feature, however, is that the chuck is hydraulically operated. Hydraulic chucks reduce the time required to both disengage the drill head from the drill rod and reengage the drill head at a different position along the drill rod.
Drill rods typically have screw-threaded male and female ends so that the rods may be threaded one onto another so as to form a drill rod string in the drill hole. The screw-threaded joints between the rods are tightened by the rotation of the drill rod string during drilling operations. Each time the rod string is hoisted from the hole, the screw threaded joint between every second or third rod must be undone. This requires that the frictional engagement between the rod ends in the joint be "broken" before the joint can be unscrewed. This is relatively inconvenient to accomplish with a conventional diamond drill, (either screw-feed or hydraulic-feed type) because the drill rod string is held by only one chuck. Thus, any rotation of the drill rods relative to the chuck (so as to unscrew a drill rod from the drill rod held in the chuck) must be the result of a rotational force applied relative to the chuck. This is typically accomplished by holding a pipe wrench in operative engagement with the rod string on the drill rod which is not held by in the chuck. The handle of the pipe wrench is rested against a portion of the drill so as to prevent the rod string from rotating, and then rotating the drill rod held in the chuck in a direction which breaks the joint and unscrews the screw threaded joint. Further, because of the location of the slightly oversized joint and knobbed thread adaptor between the rod string and the core barrel, the conventional chuck cannot be used to grip the core barrel while the last rod of the rod string is removed. This is because the chuck will not accommodate the slightly oversized joint. Consequently, the core barrel must be manually held above the drill hole once the last of the drill rods are removed from the core barrel. This is a difficult and potentially hazardous task.
U.S. Pat. No. 4,429,753, Cushman, issued Feb. 7, 1984, illustrates a simultaneous rotation and pull-down/pull-up mechanism for use on drill pipes. The drill incorporates feed rollers which grip the drill pipe between concave recesses on the rollers. The feed rollers are held in a superstructure which rotates so as to rotate the drill pipe. The rollers are aligned so that rotation of the rollers raises or lowers the drill pipe. The drill pipe may thus be rotated as it is being raised or lowered. The Cushman device has the serious disadvantage that the chuck will not automatically accommodate varying diameters of drill pipe. Further, the use of a plurality of tiers of wheels is not suggested. In view of the non-adjustability of the chuck, Cushman did not envisage an adjustable chuck using a plurality of tiers of chuck jaw wheels that would enable the retention of a core barrel in a lower tier while allowing removal of the rod string using an upper tier.
Cushman also fails to take into account the magnitude of the rotational force required to rotate a drill rod string on a drill hole. The magnitude of the force and torque required to be applied to a rod string in order to manipulate the rod string in a drill hole prohibit the use of "operative frictional engagement" through concave wheel surfaces as described by Cushman. It has been found that in order to take advantage of the bearing and shear strength of the rod steel so as to apply the required torque, it is necessary to penetrate many points on the surface of the rod with teeth on a chuck jaw wheel to a depth of up to 0.045 in. In this manner, sufficient force can be applied so as to manipulate the drill rod string in the drill hole.
The mechanism described by Cushman further fails to provide a means for positively locking the drive rollers and preventing them from turning when this is required, such as when the rod string is part way up the hole when the rods are being pulled. At best, the device described by Cushman would rely on the pull-down/pull-up hydraulic motor to provide a brake force. If this motor were to leak fluid, as hydraulic motors are prone to do, especially when they are approaching the end of their useful life, or if the conduits supplying fluid to the motor were to break, a relatively common occurrence, then the drive rollers would be free to rotate, allowing the disconnected rod string to fall down the hole.
Of particular importance is the fact that Cushman does not provide a means for applying rod-string gripping force when the drill is not rotating. Torque must be applied for operative frictional engagement. This is unsatisfactory, because when the drill is stopped, there should be some means of gripping the rod-string to prevent its falling into the drill hole.
U.S. Pat. No. 2,002,387, Bannister, issued May 21, 1935, discloses a positive displacement rotary hydraulic motor which is mounted concentrically on a drill pipe. The Bannister device requires that the circulating wash fluid, used to flush the rock debris from the drill face, be used to drive the rotation of the drill motor. The motor is located in proximity to the drill bit, that is, it is located at the bottom of the drill hole. The use of independent hydraulic vane motors for independently rotating or braking the rotation of tiers of chuck jaws is neither taught not suggested. Further, the use of hydraulic vane motors to drive chuck jaw wheels is neither taught nor suggested.